Originally Posted by Shamrock

Thanks. But I googled it already and I understand the way it is measured. That doesn't answer what the difference between the 0w40 and the 5w30 is besides cold start and high temp ratings. Does the latter have esters and the former not. That is not explained when reading about viscosity. If the former causes valve chatter in the z it doesn't also do the same in the GT-R?
One wouldn't recommend Pirelli tires for a Prius because there is no benefit equal to the extra paid for the tire but I am sure that the Pirelli is a better tire than the stock. Perhaps Nissan recommends the 5w30 for the Z because there is no real need for the 0w. The question again is what is the better oil?